Preparation and Thermoelectric Properties of LaGd1+xS3 and SmGd1+xS3

Thermoelectric materials are attractive since they can recover waste heat directly in the form of electricity. In this study, the thermoelectric properties of ternary rare-earth sulfides LaGd1+x S-3 (x = 0.00 to 0.03) and SmGd1+x S-3 (x = 0.00 to 0.06) were investigated over the temperature range of 300 K to 953 K. These sulfides were prepared by CS2 sulfurization, and samples were consolidated by pressure-assisted sintering to obtain dense compacts. The sintered compacts of LaGd1+x S-3 were n-type metal-like conductors with a thermal conductivity of less than 1.7 W K-1 m(-1). Their thermoelectric figure of merit ZT was improved by tuning the chemical composition (self-doping). The optimized ZT value of 0.4 was obtained in LaGd1.02S3 at 953 K. The sintered compacts of SmGd1+x S-3 were n-type hopping conductors with a thermal conductivity of less than 0.8 W K-1 m(-1). Their ZT value increased significantly with temperature. In SmGd1+x S-3, the ZT value of 0.3 was attained at 953 K.